Many rapid prototyping machines form a solid model, such as a model of a mechanical layers of the part on top of one another. An overview of currently available rapid prototyping technologies is found in "Rapid Prototyping Report", vol. 2, CAD/CAM Publishing, Inc. (March 1992). Reference is also made to an article entitled "Rapid Prototyping Systems", Mechanical Engineering, April 1991, pps. 34-41, which describes various rapid prototyping systems, and to an article entitled "Rapid Mold-Making for Investment Casting", Mechanical Engineering, November 1992, pps. 49-51. In general, rapid prototyping encompasses several techniques, including stereolithography, selective laser sintering, solid ground curing, fused deposition modeling, laminated object manufacturing, and photosolidification.
The following U.S. Patents are exemplary of various types of computer-controlled three dimensional object fabrication systems:
U.S. Pat. No. 4,575,330, "Apparatus For Production of Three-Dimensional Objects by Stereolithography", (Hull); U.S. Pat. No. 4,665,492, "Computer Automated Manufacturing Process and System" (Masters); U.S. Pat. No. 4,734,021, "Machine For Building a Dome or Sphere" (Maddock); U.S. Pat. No. 4,749,347, "Topology Fabrication Apparatus" (Valavaara); U.S. Pat. No. 4,752,352, "Apparatus and Method For Forming An Integral Object From Laminations" (Feygin); U.S. Pat. No. 4,752,498, "Method and Apparatus For Production of Three-Dimensional Objects By Photosolidification" (Fudim); U.S. Pat. No. 4,801,477, "Method and Apparatus For Production of Three-Dimensional Objects by Photosolidification" (Fudim); U.S. Pat. No. 4,844,144, "Investment Casting Utilizing Patterns Produced By Stereolithography" (Murphy et al.); U.S. Pat. No. 4,857,694, "Method and Apparatus For Automatic Vapor Cooling When Shape Melting a Component" (Doyle et al ); U.S. Pat. No. 4,915,757, "Creation of Three Dimensional Objects" (Rando); U.S. Pat. No 5,031,120, "Three Dimensional Modelling Apparatus" (Pomerantz et al.); U.S. Pat. No. 5,038,014, "Fabrication of Components By Layered Deposition" (Pratt et al.); U.S. Pat. No. 5,059,266, "Apparatus and Method For Forming Three-Dimensional Article" (Yamane et al.); and U.S. Pat. No. 5,121,329, "Apparatus and Method For Creating Three-Dimensional Objects" (Crump).
When fabricating a solid model of an object, such as a mechanical part, it is often sufficient and expedient to build only a hollow shell of the object without filling the interior. Thus, given a three-dimensional solid geometric model of an object, it is necessary to compute several planar slices of a shell of the object so that each slice can be fabricated by the system in sequence. However, computing the shell of the solid first before slicing it into several layers is generally undesirable in that a significant amount of time required to compute the shell of a three-dimensional solid.
It is thus one object of this invention to overcome this problem by combining the slicing and the shelling operations, and to interleave the computing task with the part building task.
It is a further object of this invention to provide an object fabrication system that operates in a pipelined manner by computing a next slice of a shell of a solid in parallel with the fabrication of a previous slice.